(676c) High-Pressure Electrochemical CO2 Capture and Reduction to Formic Acid

Electrochemical carbon dioxide reduction (CO2RR) to valuable fuels and chemicals has represented a promising carbon utilization technology. Highly selective catalysts and electrochemical devices have been demonstrated to efficiently reduce CO₂ into formic acid but suffer kinetically when applied with dilute CO₂ sources. Therefore, we present high-pressure CO₂ (>1 atm) as a method to boost electrocatalytic activity and stability. High pressures can enhance CO₂ coverage on the catalyst’s surface to convert dilute sources of CO₂ (< 10 mol%), bypassing energy-intensive upstream CO₂ purification. Here, we show that a stream of 10 mol% CO₂ can achieve a 15.8% greater formic acid Faradaic Efficiency (FE, up to 91.2% total) at 100 mA cm^-2 when pressurizing the gas stream to 5 atm. We also reach a formic acid FE of 81.0% utilizing 5 mol% CO₂ at 10 atm, attaining a 33.2% FE improvement from 1 atm. With this enhancement, we demonstrate the stable performance of 5 mol% CO2RR at 20 atm and 50 mA cm^-2 with >70% formic acid FE for up to 90 hours. Leveraging a porous solid electrolyte (PSE) reactor design with this high-pressure approach, we obtain a stream of high-purity formic acid. Simultaneously, we benefit from CO₂ capture via the crossover of (bi)carbonate ions formed at the catalyst-membrane interface, allowing neutralization and release of high-purity CO₂ gas from the middle layer. At 50 mA cm^-2 and elevated pressures, we detected the crossover of carbonate and bicarbonate ions, rather than only carbonate species, improving the electron efficiency of carbon capture.